Britney Spears Celebrates Her 35th Birthday Surrounded by Fans — and Lance Bass

Britney Spears celebrated her 35th birthday surrounded by her fans at 102.7 KIIS FM's Jingle Ball in LA on Friday night. Not only did she deliver an incredible performance of a medley of her hits, including "Slumber Party" and "Womanizer," but the event's host, Ryan Seacrest, surprised the singer by coming out on stage with a giant three-tier birthday cake and leading the audience to sing "Happy Birthday."

Later that night, Britney uploaded a video from the show on Instagram, writing, "Thank you for the sweet birthday wishes! Had an amazing day. Love you all 💖💖💖 #KIISJingleBall." Lance Bass, who also happened to be at the concert, shared a photo of him and Britney on Instagram on Saturday and captioned it, "It's been a minute since I've spent a birthday with this one! Good to know we still like rips in our jeans. 😜@BritneySpears @MichaelTurchin #BirthdayGirl #JingleBall." It's safe to say that Britney had one hell of a birthday.